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Circle skirt maths - explained!

 

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How many times in Maths class did/do you ever wonder when in the hell you'd actually need to know equations like this in real life? Well, to my dismay, it turns out that when you like to make stuff, Maths is kind of fundamental. Especially when it comes to making circle skirts. One of the easiest and quickest garments you can whip up on your machine, provided you can first figure out the radius of your waistline circumference... Ugh. Fear not, my mathematically challenged friends - we have figured it out for you. And made some pretty skirts along the way!

***Update - we made an app! Now you can leave the pesky sums to us and concentrate on the best part - sewing!***

Ready class? Then let's begin.

We're going back to GCSE Maths here guys. Remember pi?? That crazy 3 with endless decimal places is what we need to figure out the radius of our waistline circumferences. And why exactly do we need to know the radius? We need the radius in order to measure, mark out and cut the perfect little circle -that will be our waistline- onto the fabric. Without the radius, the only way to mark out the curve would be by shaping your measuring tape into a quarter circle on your folded piece of fabric (this ad hoc method I wouldn't even suggest to lazy stitchers as the results would inevitably be inaccurate, leading to a whole lot of time consuming fixing and tweaking and hair pulling and fabric wasted...).

For each type of circle skirt, be it full circle, half circle or quarter circle, the mathematical equation we need in order to find out the radius will be slightly different. Before we look at each one individually, we first need to know the foundation equation: Circumference (c) + two lots of seam allowance (3cm) ÷ ∏ (3.14) = diameter (radius × 2). We'd also like to point out now that we will be using metric measurements ie. centimetres, not inches. Nothing against Imperial, only that our brains simply can't cope with Imperial decimals, what with them being in eighths as opposed to tens...!

A note about seam allowance: seam allowance needs to be added on to both your waistline seam and side seams. For the waistline, we will be subtracting 1.5cm from your final radius measurement. For the side seams, we add 1.5cm for each raw edge to be seamed to your initial waistline circumference measurement: half and quarter circle skirts will have only one back seam so add 3cm to your waistline; a full circle skirt cut from 2 pieces will have 2 side seams so add 6cm altogether).

Full circle skirt

Let us begin by pointing out that it is unlikely you will be able to cut a whole circle skirt from a standard piece of 45" width fabric (unless making a miniskirt). The following diagram assumes that you will be cutting 2 semi-circles and joining them at the side seams, with your zipper inserted into one of those side seams - please see our invisible zipper tutorial when you get to that part!

by hand london - circle skirt maths

Example: Your waistline measures 66cm (equivalent of a 26" waist). You are making a full circle skirt from 2 semi circles so you need to factor in the 4 raw edges that will be your 2 side seams. 66cm (C) + 6cm (4SA) = 72cm. 72cm ÷ 3.14 =  23cm (diameter). (23cm ÷ 2) - 1.5cm (waistline seam allowance) = 10cm (radius).

Tip: cut a piece of string the length of your final radius measurement and holding one end at the corner, use it to accurately mark out your curve.

Half circle skirt

Our waistline measurement now becomes a semi-circle, so in order to find the radius with our little equation we need to double the waist measurement.

by hand london - circle skirt maths

Example: (66cm x 2) = 132cm (2C) + 3cm (2SA) ÷ 3.14 = 43cm (diameter). (43 ÷ 2) - 1.5cm (SA) = 20cm (radius).

Tip: before hemming your circle skirt it's a great idea to put it on a mannequin and leave it to "drop" overnight. Seeing as parts of a circle skirt hang on the bias, they'll need some time to stretch out naturally so you can then sew an even hem. If you don't give the fibres time to drop, you'll end up with a wavy, uneven hem line.

Quarter circle skirt

Just as we doubled the waistline as we halved the circle skirt, so we need to quadruple the waistline for a quarter circle skirt. The following diagram shows the quarter circle piece being cut from a single piece of fabric, no fold.

by hand london - circle skirt maths

Example: (66cm x 4) + 3cm (2SA) = 267cm ÷ 3.14 = 85cm (diameter). (85 ÷ 2) - 1.5cm (SA) = 41cm (radius).

Phew... Broken out in a bit of a mental sweat there guys, and words like radius and circle have lost all meaning. We hope this has fully explained the maths behind constructing circle skirts and their variations - if not, let us know and we'll do our best to clarify anything further. We leave you with the pretty fruits of our experiments...and one final tip: hemming a curve can be tricky; try our rolled hem tutorial for a quick, slick finish!

Over and out x

  • Elisalex de Castro Peake
  • appDIYsewingskirttutorial

Comments on this post ( 54 )

  • Jul 12, 2014

    hi there! :) it’s a great tutorial but i want ask about the hem and seam allowance that will add with the skirt length. What is suitable measurement of hem and seam allowance i should add on? thank you! :D

    — Faatihah

  • Jun 10, 2014

    Love the app but can I ask is there a way of adding in the variable of your height? Or waist to floor length…I’m only 5ft1 and I’m wondering if maxi will be too long.

    — LadyD

  • Jun 09, 2014

    Hi Nimsay, we’re definitely due an update of the app so we’ll be sure to include your suggestion – thank you! x

    — Elisalex - By Hand London

  • Jun 09, 2014

    Lovely! Wish the app could be used for plus sized ladies.

    — Nimsay831@gmail.com

  • May 22, 2014

    I love these skirts, especially the full circle. Would really like to make it with a wide panel/waistband above, do you think that would work?

    — Jo Cobbett

  • May 21, 2014

    Ah ok I get it now. Thanks. It helps that I’ve just drafted a skirt to see how it looks.

    Thanks for the great tutorial.

    — Lyn

  • May 21, 2014

    This post is awesome!

    My only complaint is that your app says I can’t make a full maxi skirt- you assume all us ladies are tall :P

    for a shorty like me it will work… wonder if you can update your app so that we can input the length of our legs… mine are short! oh so short!!!!!!!

    — Carey

  • May 20, 2014

    Hi Lyn – that final 1.5cm seam allowance subtracted is to account for the waistline to waistband seam. Hope this makes sense! x

    — Elisalex - By Hand London

  • May 18, 2014

    Hi. Why do you subtract that 1.5cm seam allowance? I don’t get it?

    — Lyn

  • May 14, 2014

    This is a great tutorial for circle skirts.. Thanks for sharing. Just one question, if I were to add an elastic waistband to a quarter circle skirt., does the radius remain the same or should I add more for ease? I’ll be using a jersey fabric btw.

    — Trudy

  • May 11, 2014

    Super handy, thanks! Will definitely try this))

    — Amy

  • May 10, 2014

    Hi Sadaya,

    Oooh an extra full more-than-circle skirt would be amazing! You would definitely need to adjust the radius however. For example, if you were making a double circle skirt, you’d need to half the radius you’d be using for a regular full circle, and for a circle and a half, it would be 75% of your regular full circle radius.

    I hope this makes sense!

    x

    — Elisalex - By Hand London

  • May 09, 2014

    What if you want to go beyond full circle for super spin—like a circle and a half or double circle, can you just add panels the same or should you adjust the radius and waistline according to a certain formula to avoid bunchy waist?
    Thanks,
    Sadaya

    — Sadaya Zimmerle

  • Apr 24, 2014

    Hi Adrienne, this really all depends on what fabric you’re planning to sew to your leotard. I’m assuming that the leotard is stretchy jersey/lycra? You’ll really need to make the 1/4 circle skirt from a similar fabric, which will give and stretch just as the leotard does, and in which case you won’t need to add on any extra ease. However, if you’re planning to make the skirt from a woven fabric – which I would suggest you don’t! – then you would need to add a significant amount of ease so the skirt’s waistline can stretch enough to pull over your hips as you put the leotard on. You’d end up with a gathered skirt stitched onto your leotard which would massively distort the shape of your leotard’s waistline. Hope this all makes sense! x

    — Elisalex - By Hand London

  • Apr 24, 2014

    Hi! I will be sewing a quarter circle skirt to a leotard, should I add a couple inches to my waistline so that I have some room for “give”/stretch on the waist?
    Thanks!

    — Adrienne

  • Apr 23, 2014

    Salwa, you may need to use sheeting fabric

    — shopping sophie

  • Apr 22, 2014

    Hi, I don’t anything on here regarding a hem. Would I just add the hem measurement to the desired length of the skirt?

    — Ashley Dunn

  • Apr 07, 2014

    Hello,

    I’ve done some circle skirt maths for drafting a circle skirt to attach to an existing bodice pattern…would be interested in hearing others’ feedback on my sums :)

    http://belgianseams.blogspot.be/2014/04/mustard-and-maths.html

    — Emily - Belgian Seams

  • Mar 19, 2014

    Hi Carmen, I’m afraid that unless your fabric is a striped circle (like a target), or you’re prepared to cut and match maaaaany panels, you’re not going to be able to get a circle skirt with stripes going all the way around… You’re much better off making a gathered skirt from a long rectangle so that the stripes all go in the same direction. You can check out our gathered skirt DIY here – http://byhandlondon.com/blogs/by-hand-london/11628445-diy-gathered-skirt

    Hope this helps!

    — Elisalex - By Hand London

  • Mar 19, 2014

    I have a veeery striped fabric that i want to go all the way around my skirt nicely but have no idea how to cut it! please help

    — Carmen Fernandez

  • Mar 10, 2014

    Hi Salwa – I’m afraid you’re going to have one hell of a time looking for jersey in a 230cm width! I’m pretty sure it simply doesn’t exist… You’re only solution for making a maxi full circle skirt is to cut it in multiple panels. You might be able to cut 4 quarter circles out of a 150cm width fabric – just remember to add on the seam allowances for the extra side seams! Hope this helps x

    — Elisalex - By Hand London

  • Mar 09, 2014

    Hiya,
    Great explanation and step by step. I want to make FULL maxi circle Skirt.
    I am unable to find fabric that wide in the UK. Any suggestions on how else I could make it. From waist to feet I measured 115cm so I would need 230cm wide fabric. And they only sell that width of fabric for curtains and furnishings. Most dress fabrics are 150cm wide And that would be waaay to short for what I need.
    I am wanting a heavy weight Soft Jersey in that width. Any tips on where to look? any online stores in the UK?
    Thank you

    — Salwa

  • Feb 27, 2014

    Hi Kerry – hmmmm that sounds like a bug in the app…. a 1/4 circle maxi skirt should fit nicely on a 60" width fabric. If I were you, go by the given radius and then measure out the length manually. Good luck (and we’ll get that bug sorted ASAP!)

    — Elisalex - By Hand London

  • Feb 25, 2014

    I love the look of the quarter circle maxi in the last photo. When I use the Circle Skirt App, it tells me that my skirt will not fit on a 60" piece of fabric. How did you achieve that skirt? I am a novice when it comes to clothing construction, so any insight you have would be marvelous. Thank you!

    — Kerry

  • Jul 28, 2013

    Hi Jessica,

    You do that because 1.5cm is your waist seam allowance. Taking that away from your radius means that you end up with the correct waist measurement once you’ve sewn on your waistband. Hope this makes sense!

    — byhandlondon

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